Study of luminescence from GaN: Tb³⁺ Powders and thin films deposited by MOVPE and PLD methods

Due to the recent commercial interest in nitride-based optoelectronics and rare-earth emission in nitride materials, the structural and optical characteristics of GaN: Tb³⁺ powders and thin films have been investigated in this work. The powder samples were made using a three-step solution method. Pulsed laser deposition (PLD) and metallorganic vapor phase epitaxy (MOVPE) methods were utilized for depositing GaN: Tb³⁺ films on sapphire substrates. The GaN powders with activator concentrations up to 8 atom % exhibited Tb³⁺ luminescence due to the D 3,4 5 → Fj7 transitions under cathodoluminescence (CL) as well as under 243 nm photon excitation. Both near-band-edge emission and activator emission have been observed in PLD thin films made from the corresponding GaN: Tb3+ powders. X-ray diffraction revealed polycrystalline PLD thin films with a preferred growth direction along the c axis, while scanning electron micrographs showed rough film morphology with submicrometer particles. CL emission from Tb³⁺ accompanied by near-band-edge emission and defect emissions from the GaN host was observed for the MOVPE films made using tris(2,2,6,6-tetramethyl-3,5- heptanedionato)terbium but not films made with tris(isopropylcyclopentadienyl) terbium. Despite visible luminescence from Tb3+ in GaN powders and thin films, no energy transfer from the host to activator ions was observed. This suggests that Tb3+ is unlikely to fluoresce if used in a GaN-based optoelectronic device.